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Topic: Replace chip (PCB) in usb midi keyboard with arduino (Read 5079 times) previous topic - next topic

Macola

My M-audio keystation 61 midi keyboard stopped working and the culprit is on microcontroller which is responsible, among other things for usb connection. That chip costs 1$ but I've been told that the original code is protected and can't be find and the whole original pcb replacement is to costly. The whole circuitry is very simple: there are 2 chips, first one (W78E052DDG) is connected to all of the keys matrix and their velocity calc (24 input pins). Then the result is sent to another chip (micro controller C8051F320) via 14 pin jack, which is doing USB/midi communication.

It should be fairly easy to replace second pcb with arduino considering that it gets sorted out signal from keyboard velocity chip? Right?

Or maybe to replace both chips and connect 24 pins matrix directly to arduino?

Grumpy_Mike

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Right?
If you say so but I doubt it. Many of those custom chips have hardware built into them that the Arduino dosn't.

DVDdoug

It might be possible, but if you've never made a MIDI project before, I'd recommend building a simple test/experiment project first...   Maybe something that sends a couple of MIDI notes/commands with little or no user input.

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It should be fairly easy to replace second pcb with arduino considering that it gets sorted out signal from keyboard velocity chip? Right?
"Sorting out" those signals could be tricky, especially considering that the keys are velocity-sensitive.  (It's not a simple "digital" matrix.)

It should be possible to replace all of the electronics, but you'll have to multiplex the (analog) key-inputs in order to get enough inputs.

I wouldn't say wiring-up 61-keys (and other controls?) and everything would be "easy", especially if you don't make a custom PC board or two.   And, then there's the programming.    By the time you're done you'll have lots of hours into this thing and it might not be as good as the original, and you may put more money into it that you anticipate.   So, I'd recommend you only do this if you're doing it for fun, or if you want to add some features/functions that you can't find in a commercial keyboard.

Macola

Thanks for the replies. I am aware of the things you've said. I am not an expert in this area and the things would easily get tricky at some point. On the other hand there are many diy project on line to make a midi keyboard out of any cheap non usb/midi keyboard just by adding some electronics. I don't have an intention to restore all the original functions, which are not many in this case anyway. Just to make keyboard basically work connected to pc via usb. And, yes it would be a joy project.

Many people recommend arduino as there are available libraries. Surprisingly, there are also many specialized chips (with free open code) exactly for this purpose - to make midi keyboard out of any old keyboard. For example E510 - 128 keys velocity sensitive keyboard scanner. So I thought it would be worth giving it a shot. It's just that atm I lack experience.

I this case of mine both chips are just simple general purpose microcontrollers similar to the arduino ones. One is doing keyboard scanning/multiplexing the other has usb controller. Each cost 1$. The problem is the code in them. It's proprietary.

This, for example, looks pretty straightforward: http://www.geocities.ws/JDPetkov/Hardware/mkcv96/mkcv96.htm


Grumpy_Mike

OK that is fine as long as those are your expectations.
The most common way for a velocity sensitive keyboard is to have two switch contacts per key. When a key is pressed first one contact is broken and then the other one is made. The time between make and break is the velocity data.

The complication arises because you are trying to measure the time of multiple contact changes at the same time.

Macola

I took apart my keyboard and realized the type of matrix and velocity. Classic matrix and the velocity is double switches per key but both getting contact when pressed just in a slightly different time depending on velocity/force.

Also found a guy who did exactly what I want - connected key matrix of broken keyboard (same type matrix) to arduino. He actually has connected flat cable of the keys directly to arduino mega cuz it has sufficient input pins. As far as I can see on the pic he has even physically connected it directly w/o any additional cables/adapters.

And the code is exactly for velocity keyboards. How cool is that.

I am not sure if it's legit to link that here?

Grumpy_Mike

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I am not sure if it's legit to link that here?
If it is on the internet then you can link it.

Macola

Ok, I am a bit late cuz I wanted to give it some try first, and I did.

The project I was referring to is: https:

I managed to make my mega act as USB MIDI instrument by burning special firmware in, but the above sketch is not working.

Then, I tried an example midi library that comes with arduino IDE and that works! It generates sequence of midi notes and all the PC audio software plays it.

So it's about the sketch OR me not connecting pins right. I did check keyboards flat cable connectors with a multi meter and the situation is pretty clear. There are 8 x (8x2) matrix. The 8x2 is cuz double switches for velocity. Tbh, I didn't connect whole matrix but just some keys, but that should work? I didn't change pins in the sketch just connected the key according to the original code. Nothing happens when I press that key. Shouldn't there be an event if any row/column combination is switched on?

Another thing, there is a thick black wire. That is a ground? Tried to connect it to ground pin on digital pins row but no change.

Macola


Grumpy_Mike

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The project I was referring to is: https://github.com/oxesoft/keyboardscanner
It is not very detailed is it? Without a schematic it is hard to know what is going on.

I would forget that code for the moment and concentrate on testing if you can get the key switches to be read. So forget about the MIDI and the scanning of all the keys and just concentrate on one key. Write a bit of simple code to do that and use Serial.print at a standard speed to send stuff out to the console so that you know you are detecting stuff.


Macola

Exactly my thoughts! Build it up gradually. I did, already, the basic test of detecting pins by using example sketch in the DIO2 library (it's the included library in that project that makes the use of pins easier and supposedly speed it up). That code uses Serial.print ant it works. When each pin is connected to ground I can read them on serial monitor.

What I've noticed as a potential problem is that it may be reverse input - output pins. In the scanner code it's 16(8x2)input pins x 8 output pins, BUT by the orientation of keyboard diodes it should be other way around? Does that make sense?  EDIT: scratch this paragraph, it's the way it should be

I tried to reverse pins on one key but no luck.

Macola

Ok this is getting seriously weird. Let me just show you, cuz you need to see it to believe it:

https://www.youtube.com/watch?v=6h_6V134Ty0

I've got me an air piano!

Now seriously, what the heck!? Why so much induction? At first I thought there is some mechanical failure with the pins, but then realized that I don't even need to touch it to play a sound. Especially when I connect a wire to just one pin it gets overloaded and plays a bunch of notes.

My guess there is something oscillating to fast. Looping fast or something?

On the bright side it seems that I get it to work kinda. Just need to calm it down.

Grumpy_Mike

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Now seriously, what the heck!?
This is normal. It is known as a floating input see this http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

Can you draw a schematic of what you think the project might be.

Macola

The sketch I used when I've got the strange behavior is other than the one I originally posted about. This one uses demultiplexers like most of other project, so I just tried to make it work with no demiltiplexers code and got that.

So I am back to the project that suppose to be right the stuff that I need, cuz it's for the velocity matrix keyboard and for arduino mega. But it refuses to work. I actually bought the mega just because I've saw that project.



Grumpy_Mike

Sorry but the code means little without a schematic.

You first have to verify the hardware before delving into driving it otherwise you don't know if the problem is hardware or software.

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